Infra-redradiation (also
called thermal radiation)transfers heat between allobjects.
The frequency at which
an objectemits electromagnetic radiation
is called
its principle
frequency.
The principle frequency
increases as the temperatureincreases.
The Sun is hotter than
the Earth and so has a higher
principle frequency.Infra-redradiation is an electromagneticwave and can travel
through a vacuum.
Heat from the Sun reaches us through
the vacuum of space
by travelling as infra-redradiation.

An object can absorbradiation
(take it in),emitradiation (give it out) and
reflectradiation.

The hotter an object,
the faster it will emit infra-redradiation.Hotterobjects will emitinfra-redradiation fasterthan they absorb it from colderobjects around them.Colderobjects will absorbinfra-redradiation
faster than they emit it to hotterobjects around them.
In this way heat is transferred from
hotter to colder
objects.
An object whose temperature does not
changeemits infra-red radiation at the
samerate
as it is absorbed.

Objects that are at the sametemperature as
each otherabsorb, emit and reflectinfra-red
radiation at different
rates
depending on the type
of surface that the
object has.